Method and apparatus for compression molding closure liners

Abstract: A method and apparatus for compression molding closure liners wherein a set of tooling including a first assembly (35) and second assembly (36) which are movable toward and away from one another. The first assembly (35) of tooling has a liner forming member and a closure engaging sleeve thereon and the second assembly (36) has a closure supporting pad (41) thereon. A cam (37) is associated with the first assembly of tooling for moving the closure engaging sleeve into engagement with a closure and the liner forming member into position for compression molding a charge of plastic extrudate in the closure when it is supported on the closure supporting pad (41). A gas cylinder (39) is associated with the closure supporting pad providing a predetermined controlled pressure that determines the compression molding force on the plastic. In a preferred mode, a plurality of sets of tooling are provided in circumferentially spaced relation to one another on a turret.

Description: The invention relates to a method of compression molding liners in closures according to the preamble of claim 1 and to apparatus according to the preamble of claim 7. In a method and apparatus of said kind (EP-A-0 037 651 = US-A-4,388,058) the closure together with the laminar material is put onto the surface of a support and a tooling assembly is moved by a fixed stroke onto the liner material to form the liner. The tooling assembly comprises an inner punch and an outer bushing, both connected to a main body which can be raised and lowered. Furthermore, the outer bushing can be driven by a piston for the fixed stroke. The support does not yield. In producing a shaped body of plastic material (EP-A-0 175 642 = US-A-4,735,761) an upper and a lower tool member are closed as by cams and a pressure fluid cylinder is activated to apply the pressing force onto the plastics material. The lower tool in the form of a die does not yield. The form of liners in closures is also known from US-A-2,072,536, 2,930,081, 3,827,843, 4,274,822, 4,312,824 and 4,497,765. One of the problems in compression molding of liners is that of controlling the molding force when molding liners directly into a closure such that sufficient molding force is used to fill the required seal volume and not produce shorts and, at the same time, to limit this same force to avoid flashing of the liner. This force should be consistent and equal on each of all toolings to avoid process variability. The use of compression springs to control this force would not be consistent from tool to tool due to the variability of the rating of the springs and due to the inevitable fatigue that would be induced after substantial length of running. Further, means to readily adjust the molding force of all toolings with one adjustment of system pressure is desirable. Among the objectives of the present invention are to provide a method and apparatus for compression molding liners in plastic closures wherein the molding pressure on the charge that is being shaped to define the liner is accurately controlled; wherein when an array of tooling is provided, each set of tooling functions independently of the other; wherein the forming pressure can be readily changed; and wherein the tooling can be readily assembled and removed. The method and apparatus for compression molding closure liners in accordance with the invention, are defined in the independent claims 1 and 7 respectively. Preferred embodiments of the method and apparatus are defined in claims 2-6 and 8-20 respectively. Description of the Drawings FIG. 1 is a front elevational view of an apparatus embodying the invention. FIG. 2 is a top plan view, parts being broken away. FIG. 3 is a fragmentary vertical sectional view through a portion of the apparatus. FIG. 4 is a fragmentary plan view taken along the line 4-4 in FIG. 3. FIG. 5 is a fragmentary sectional view on an enlarged scale of a first or upper assembly of tooling shown in FIG. 3. FIG. 6 is a fragmentary vertical sectional view on an enlarged scale of a second or lower assembly of tooling shown in FIG. 3. FIG. 7 is a plan view of a nitrogen manifold utilized in the apparatus. FIG. 8 is a sectional view taken along the line 8-8 in FIG. 7. FIG. 9 is a sectional view taken along at the circle 9-9 in FIG. 8. FIG. 10 is a fragmentary sectional view taken along the line 10-10 in FIG. 7. FIG. 11 is a fragmentary sectional view taken along the line 11-11 in FIG. 7. FIG. 12 is a fragmentary sectional view taken along the line 12-12 in FIG. 7. FIG. 13 is a fragmentary side elevational view of cams utilized in the apparatus. FIG. 14A is a fragmentary view of the upper cam shown in FIG. 13. FIG. 14B is a view of the lower cam shown in FIG. 13. FIG. 15 is a fragmentary plan view of a portion of the apparatus shown in FIG. 1. Description Referring to FIGS. 1-3, the apparatus embodying the invention comprises a base 30 on which a column 31 is fixed. A carousel or turret 32 is rotatably mounted on column 31 by upper and lower bearings 33, 34. The turret 32 supports sets of tooling comprising a first or upper assembly 35 of tooling and a second or lower assembly 36 of tooling circumferentially spaced about the turret 32. An annular fixed cam 37 is provided and is associated with the first assembly 35 of tooling, as presently described. Bach second assembly 36 of tooling further includes an annular gas manifold 38 that supports a plurality of circumferentially spaced gas cylinders 39. Piston 40 of gas cylinder 39 acts against a closure supporting pad 41 in the lower or second set of tooling 36 through an intermediate member 78 (FIG. 6). The manifold 38 and gas cylinders 39 are charged with an atmospheric gas, preferably nitrogen, at predetermined pressure. Referring to FIGS. 5 and 6, each first assembly 35 of tooling comprises an annular support 50. An actuator 51 is movable vertically in support 50 by engagement with a cam follower roller 52 on the actuator 51 with cam 37 to move a liner forming plunger assembly 53 mounted on the actuator 51 downwardly through a fixed stroke. A closure engaging sleeve 54 is provided about the liner forming tool 53 and is yieldingly urged axially outwardly and downwardly by circumferentially spaced springs 55 engaging pins 56. A flange 57 on the tooling limits the outward movement by engagement with a flange 58 on an outer fixed sleeve 59. Coolant is provided to the interior of the liner forming plunger 53 and circulated therethrough through inlet 60 and outlet 61 connected, in turn, to a distributor 63 mounted rotatably in the column 31 and rotated by a gear 64 such that the distributor and associated hoses, not shown, move with each set of tooling 35 (FIG. 3). Referring to FIGS. 3 and 5, the closure supporting pads 41 are mounted in a support ring 70 that, in turn, is mounted on a radial flange 71 on the turret 32. The support ring 70 is secured to flange 71 by bolts 72. The annular support 50 for the first assemblies 35 is supported on the support ring 70 by bolts 73 (FIGS. 5, 7). Referring to FIGS. 3 and 6, annular gas manifold 38 is mounted on the underside of support ring 70 by bolts 75. The gas cylinders 39 are mounted on the gas manifold 38 and extend into cylindrical openings 76 that extend downwardly. Each gas cylinder 39 has an annular flange 77 that engages the upper surface of gas manifold 38 and cooperates therewith to form a seal. The piston 40 of each cylinder 39 engages an intermediate member 78 which, in turn, engages the closure support pad 41. A light spring 79 urges the pad 41 upwardly to facilitate loading of a closure C in position on the pad 41. A retaining ring 80 held in position by bolts 80a limits the upward movement of the pad 41. Referring to FIGS. 7-12, gas manifold 38 has an inlet 81 with an associated one-way valve 82 (FIG. 12). The chambers 76a of openings 76 beneath each gas cylinder 38 (FIG. 6) are interconnected by passages 83-85 to provide a manifold chamber in the chambers 76a beneath the cylinders. The manifold chamber is provided with nitrogen at a predetermined high pressure thereby defining a manifold chamber 76a beneath each gas cylinder 39 which is at the predetermined pressure. The passages 84, 85 provide communication to chamber 76a. One or more of the chambers 76a can be provided with a pressure gauge 86 (FIG. 10) or a rupture disk 87 for pressure relief (FIGS. 8, 9 and 11). Referring to FIGS. 14A and 14B, cam 37 is positioned to lower the upper tooling 35 into position by engagement of the roller 52 on the upper tooling 35 for compressing the liner. A second cam 88 is provided for engaging a second roller 89 on actuator 51 (FIG. 5) to lift the upper tooling in order to facilitate placement and removal of closures on the closure supporting pads 41. The closures C are preferably made of plastic such as polypropylene or polyethylene and comprise a base wall and a peripheral skirt. A typical closure is such as shown in US-A-5,265,747. In operation, charges of molten plastic are fed successively to each closure C positioned in inverted position as it is moved through a worm 90 and starwheel 91. The charge of extrudate of plastic material for forming the liner may be delivered to each closure when the closure is in any position either before it enters the turret 32 or after it has entered the turret 32. As the closure C is moved by supporting pad 41 between the first or upper assembly 35 of tooling and the lower assembly 36 of tooling which supports the closure and turret 32 is rotated, the cam 37 moves the upper tooling 35 downwardly causing the sleeve 54 to engage the closure C and then move the liner forming plunger 53 downwardly through a fixed stroke to compress the charge of plastic into a liner. After the initial compression of the light spring 79, the control of the forming pressure is through the predetermined pressure on the piston rod 40 of the gas cylinder 39. Inasmuch as the pressure of the gas cylinder 39 is at a very high pressure, for example, on the order to 60 bar (850 psi) and the amount of movement is very small on the order 0.508 mm (0,020 inch) the volume of glass displaced relative to the total volume of the system is relatively insignificant. The gas volume of the manifold is thereby substantially constant and the force generated by each cylinder is substantially constant. Accordingly, the forming or compression force on the charge of plastic is accurately controlled at a predetermined pressure. After a predetermined portion of the cycle of application of a very high pressure, the cam 37 has a rise that allows the upper tool forming plunger 53 to retract sufficiently to raise the lower support plate 41 until intermediate member 78 contacts a shoulder and the support pad 41 is supported only by the spring 79. During this stage, the molding force is reduced during the plastic cure. Furthermore, it is possible to adjust the pressure in the manifold by increasing or decreasing the pressure through the inlet valve 81. It can thus be seen that in accordance with the invention, the control of mold forces within each set of compression molding tool, is independent of external compensating means. The turret or carousel is mounted on heavy duty taper roller bearings to adequately withstand the cantilevered loading of the molding force. The gas manifold 38 has cross drillings 83-85 in place to connect all the cylinders 39 to a common chamber and to a common charging port for system pressure setting. The upper tooling ring 50 is attached to the turret and has bushings to guide each upper tooling assembly 35 in the form of a cartridge and its associated inner tooling components as it is actuated downwardly by the cam roller 52 engaging the upper cam FIG. 37 (FIGS. 13, 14A and 14B). The inner tooling components include a spring loaded outer tooling components including a spring loaded outer sleeve and a directly actuated inner tooling. The upper tooling cam 37 is continuous, and with no moving sections. As the turret 32 rotates, successive sets of upper tooling are actuated downwardly toward the closure as it rests on the lower tooling plate, and the outer sleeve engages the closure seal ring and begins to compress the spring. The previously introduced extruded pellet in the closure is formed by the advancing inner plunger 53, and each inner tooling continues to advance a common fixed stroke. The advancing inner plunger creates a pressure within the melt, and this in turn results in a force transmitted to the load plate 41, which then compresses the spring until the piston rod is engaged. The gas cylinder 39 resists the force of molding until the preset limiting force is achieved, whereby the cylinder compresses to limit the molding force. The inner plunger continues to complete its fixed stroke, and during this time the mold force remains at its limiting force as preset by the gas pressure. To offload the tooling forces after molding, the upper cam has a rise, for example, of about 1,016 mm (0,040 inch) and this allows the upper tool to retract sufficiently to raise the supporting pad 41 and the load plate until the intermediate plate 70 contacts the shoulder in the tooling ring, and the tooling plate is supported only by the spring. Thus during the curing stage, the molding force is reduced. As indicated above, the cantilevered load on the turret is opposed by the tapered roller bearing mount of the turret. It can thus be seen that there has been provided a method and apparatus for compression molding liners in plastic closures wherein the molding pressure on the charge that is being shaped to define the liner is accurately controlled; wherein when an array of tooling is provided, each set of tooling functions independently of the other; wherein the forming pressure can be readily changed; and wherein the tooling can be readily assembled and removed.

Claims: A method of compression molding liners in closures (C) comprising the step of: providing a tooling assembly (35) having a liner forming plunger, a first sleeve surrounding the plunger and a second sleeve engaging the closure and surrounding the first sleeve, and a closure support; positioning a closure (C) having a charge of extrudate therein onto said closure support; moving said tooling assembly (35) by a fixed stroke in a working direction in engagement with said closure (C) and said charge of extrudate, characterized in that cam means (37) is provided for moving the tooling assembly (35) by said fixed stroke, said closure support is a pad (41) supported by a gas cylinder (39), the compression molding force is controlled by the magnitude of gas pressure within said gas cylinder (39). The method of claim 1 wherein said working direction is downwardly against the action of said gas cylinder (39) being beneath said pad (41). The method of claims 1 or 2 comprising the steps of: providing an array of tooling assemblies (35) and an array of pads (41) associated thereto along an endless path, successively supporting a closure (C) having a charge of extrudate therein on a pad (41) of said array, and moving said tooling assemblies (35) and said pads (41) past a working station where each said tooling assembly (35) is stroken by said cam means (31) into said working direction. The method of claim 3 wherein each charge of extrudate is delivered to its closure (C) when such closure has entered said endless path. The method of claim 3 wherein each charge of extrudate is delivered to its closure (C) and such closure is on its way to enter said endless path. The method of any of claims 1 through 5 wherein the tooling assembly (35) is retracted so as to reduce the molding force during a period of curing the charge of extrudate. An apparatus for compression molding liners in closures (C), comprising a support for supporting a closure (C) which has a charge of extrudate therein, a tooling assembly (35) having a liner forming plunger (53), a first sleeve surrounding the plunger and a second sleeve (54) surrounding the first sleeves and engaging the closure, and operable with a fixed stroke in a working direction to engage said closure (C) and said charge of extrudate so as to form a liner, operating means for moving said tooling assembly (35) by said fixed stroke, characterized in that said operating means comprises cam means (37), said closure support includes a pad (41) and a gas cylinder (39) having a gas pressure chamber (76a) and a piston (40) operable onto said pad (41) in a direction opposite to said working direction, and in that means (38, 81-86) for controlling the gas pressure within the gas pressure chamber (76a) is provided so that when said tooling assembly (35) is operated, said charge of extrudate is acted upon by a compression molding force which is determined by the magnitude of said gas pressure. The apparatus of claim 7 wherein said gas cylinder (39) is arranged beneath said pad (41). The apparatus of claims 7 or 8 wherein an array of tooling assemblies (35) and an array of pads (41) with gas cylinders (39) and gas pressure chambers (76a) associated thereto are arranged along an endless path, wherein means (32) for moving said array of tooling assemblies (35) and pads (41) along said endless path to a working station is provided and wherein actuator means (51), one for each tooling assembly (35), are provided for operating such tooling assembly (35) which is arrived at the working station. The apparatus of claim 9 wherein said actuator means (51) is acted upon by said cam means (37) which is arranged along the endless path for moving said tooling assemblies (35) into and out of engagement with said closures (C). The apparatus of claims 9 or 10 wherein said moving means (32) includes cooling fluid delivering means (60, 61, 63) for said tooling assemblies (35). The apparatus of any of claims 7 through 11 wherein said actuator means (51) include a plunger (53) and wherein a sleeve (54) which surrounds that plunger (53) is mounted on said actuator means (51) for engaging the closure (C) and holding it on the pad (41). The apparatus of any of claims 9 through 12 wherein said gas-providing means (38, 81-86) includes means for interconnecting (83, 84, 85) said plurality of gas pressure chambers (76a). The apparatus of claim 13 wherein said interconnecting means (83, 84, 85) is included in a manifold (38) which has a charging valve (82) for admitting said predetermined gas pressure to said gas cylinders (39). The apparatus of any of claims 9 through 14 wherein said array of pads (41) is arranged in hollows of a supporting ring (70) which is rotated by said moving means (32) moving said array of tooling assemblies (35). The apparatus of any of claims 9 through 15 wherein said array of tooling assemblies (35) is arranged in cavities of a tooling ring (50) which is rotated by said moving means (32). The apparatus of claim 16 wherein each a support sleeve (59) is inserted in each said cavity of said tooling ring (50), such that each tooling assembly (35) can be removed by vertical movement upwardly from the tooling ring (50). The apparatus of claims 16 or 17 wherein said moving means (32) is in the form of a caroussel or turret journaled on a column (31). The apparatus of any of claims 9 through 18 wherein a delivering station (90, 91) is arranged upstream of said working station along said endless path for delivering each a charge of extrudate to a closure (C) which arives at said station. The apparatus of claim 19 wherein said cam means (37) includes a lifting cam (88) for moving said actuator (51) upwardly, when each said tooling assembly (35) is adjacent said delivering station (90, 91).

Inventors: INGRAM KEITH W, INGRAM, KEITH W.
Applicants: OWENS ILLINOIS CLOSURE INC, OWENS-ILLINOIS CLOSURE INC.
Application year: 1994
Main classification: B29C70
IPC codes: B29C43, B29L31, B29C47, B29C70